Icon missing system tray
For some reason the icons from the system tray disappears or are disabled in Windows Vista, there seems no easy way to fix it. But fortunately there are always solutions...
In Windows Vista you can easily enable these notification icons. The Task bar or the Start Menu Properties dialog are accessible by right-clicking the Start icon or the tray section and selecting properties.
Check the check boxes click Apply or OK and restart the computer, your icons should be visible in the system tray section.
If you find these options to be grayed out; the most common one is the power for some reason this check box becomes grayed and you can not place the check mark on it.
Observe the image on the left, these icons are grayed out. Every secret of windows configuration and settings are stored into the registry, which you can manually edit if you know what you are looking for.
The easiest way to correct this power option is to go into the Device Manager, find the ACPI remove it, and restart the computer.
Or the long way Edit the Registry!
To solve the issue with the above scenario, you could do the following: from the run command type regeditinside the registry windows keeps the info related to the system tray.
Once in the registry perform a search for : IconStreams and PastIconsStream
Delete both: IconStreams and PastIconStream
Once Those Keys are Deleted restart the computer, the icons should come back into the system tray. If the icons are not there, right click the tray or start icon properties and check the checkboxes.
Note: if the computer is running very slow and sluggish, don't bother fixing this minor issues back up and restore the computer to factory settings or perform a clean Install-recommended.